Preparation of 2-hydroxytetrahydrofuran

ABSTRACT

An improved process for the conversion of allyl alcohol with hydrogen and carbon monoxide to form a reaction mixture containing hydroformylation products of 2-hydroxytetrahydrofuran and/or 4-hydroxybutyraldehyde. Allyl alcohol, hydrogen, and carbon monoxide are passed, in a gaseous phase, into contact with a catalyst comprised of a solid porous carrier material containing within its pores a solution of a catalytically active metalloorganic complex dissolved in at least one ligand-forming compound, which solution has a vapor pressure of less than 1.3 mbar under the reaction conditions applied. The improved process is preferably carried out on a continuous basis.

BACKGROUND OF THE INVENTION

The invention relates to a process for the preparation of4-hydroxybutyraldehyde and/or 2-hydroxytetrahydrofuran formed bycyclization of 4-hydroxybutyraldehyde.

It is known that these compounds can be obtained by reaction of allylalcohol with carbon monoxide and hydrogen by hydroformylation in thepresence of a noble metal complex, in particular a rhodium complex.According to German Patent Application No. 2,538,364, thehydroformylation is performed batchwise as a homogeneous liquid phasecatalytic reaction wherein the rhodium complex is present as a solutionin an inert solvent. Further steps are thus required to recover thecatalyst from the reaction product.

This known method of hydroformylation of allyl alcohol also may resultin the formation of by-products such as 2-hydroxymethylacetaldehyde(formed by hydroformylation of the second position of the allylalcohol), propionaldehyde (formed by isomerization of allyl alcohol),propanol (a hydrogenation product), and polymers. The primaryhydroformylation product of this known process is probably4-hydroxybutyraldehyde, which can be converted by cyclization to2-hydroxytetrahydrofuran. Both 4-hydroxybutyraldehyde and2-hydroxytetrahydrofuran can be converted to 1,4-butanediol.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an improved method forthe hydroformylation of allyl alcohol, which method can be performedcontinuously with a high selectivity toward the desired product, withoutthe catalyst recovery problems attendent to the above-mentioned knownprocess.

According to the invention, allyl alcohol is converted with hydrogen andcarbon monoxide in the presence of a catalytically active metal complex.The conversion is performed in a gas phase in the presence of a catalystconsisting of a solid porous carrier material, in the pores of which isa solution of a catalytically active metallo-organic complex dissolvedin one or more ligand-forming compounds, which solution has a vaporpressure of less than 1.3 mbar under the reaction conditions applied.The process of the invention is ideally suited for carrying out theconversion on a continuous basis.

The hydroformylation with the improved method according to the inventionhas a number of distinct advantages. The reaction can be performedcontinuously and the recovery of the reaction product is very simple.The selectivity towards 4-hydroxybutyraldehyde and/or the cyclicderivative thereof is high, and the reaction can be performed such thatthe isomerization of the allyl alcohol to propionaldehyde is suppressed.

The temperature at which the reaction is performed must be high enoughfor both the allyl alcohol and the hydroformylation products formed tobe present in gaseous form. A temperature of between about 90° C. and150° C. is in general appropriate. A temperature of between 100° C. and130° C. is preferably applied. In this temperature range the catalystactivity is high, yet the temperature is not high enough to cause anysignificant loss of the metallo-organic complex.

The reaction can be carried out in either a fluidized bed or a fixedbed. The reaction can be effectively performed at a pressure of betweenabout 1 and 35 bar. However, a pressure of between 2 and 5 bar appearsmost preferable.

The molar ratio between the hydrogen, allyl alcohol, and carbon monoxidereactants should be generally within the range of about 2 to 10:1:2 to20. The hydrogen and carbon monoxide should be present in a molar ratioof between about 1:1 and 1:5.

Unconverted allyl alcohol and the hydroformylation products formed canbe isolated from the reaction mixture by condensation. The allyl alcoholcan then be recovered by distillation and recycled to the reactor. Inthe reactor the main product formed is 4-hydroxybutyraldehyde. However,during the condensation this 4-hydroxybutyraldehyde is almost completelyconverted to 2-hydroxytetrahydrofuran. 1,4-butanediol can be obtainedfrom either compounds by hydrogenation.

The catalyst used in this improved method consists of a solid porouscarrier material, having present in the pores thereof a solution of acatalytically active metallo-organic complex dissolved in at least oneligand-forming compound, which solution has a vapor pressure of lessthan 1.3 mbar under the reaction conditions applied.

As the carrier material, both organic and inorganic solid porousmaterials may be used. Examples of suitable carrier materials includesilica, zeolites, activated carbon and macroreticular polymers.Preferably, a carrier material is used that has a surface that isorganophilic, and that furthermore contains no groups that may promotethe formation of by-products and/or deactivate the metallo-organiccomplex. Suitable examples of such preferred carrier materials includemacroreticular polymers containing no alkali or alkaline earth metalions or acid anions; silica rendered hydrophobic by heating;silica-alumina containing no alkali metal ions; and inorganic materialssuch as silica, the acid or basic groups of which have been converted toinert hydrophobic groups by treatment with a suitable reagent, forinstance by silanization.

Organic polymers that may be considered suitable carrier materialsinclude crosslinked polyacrylates and crosslinked polystyrene,particularly the macroporous polystyrene resins crosslinked withdivinylbenzene. Since these polymers may contain ionic impuritiesoriginating, for example, from the polymerization catalyst, they shouldpreferably be thoroughly washed before being impregnated with thesolution of the metal catalyst. An advantage of using these organicpolymer resins as porous carrier materials is that they are pronouncedlyorganophilic. A disadvantage is, however, that they cannot be utilizedin a fluidized bed, and that problems may arise with the heat dischargedin a fixed bed, and they may soften at temperatures above about 150° C.

It is preferable to use inorganic carrier materials. A very suitableinorganic carrier is silica rendered hydrophobic by heat treatment at atemperature of at least 700° C. (see for this treatment S. Kondo et al,Journal of Colloid and Interface Science, Vol. 55 No. 2 (1976) p. 421).The material must be completely, or at least substantially, free ofalkali metal ions, on the one hand to prevent sintering during the heattreatment, and on the other hand to suppress the aldol condensation ofaldehydes formed during the hydroformylation. Carriers that by naturecontain acid or basic groups on their surface, such as silica,silica-alumina or alumina, can be made into very suitable carriers bytreating them with a suitable reagent to convert the reactive surfacegroups into inert groups. A silane, having at least one substituent onthe silicon atom that reacts with the reactive surface groups, can beeffectively utilized as an inertizing agent.

The dimensions of the carrier material particles may vary betweenapproximately 0.01 and 5.0 mm. Particles having a size in the range ofbetween about 0.01 and 0.1 mm are preferably used in fluidized bedapplications, whereas for fixed bed applications, a particle size ofbetween about 0.2 and 2.0 mm is preferred.

A suitable carrier material will have a pore volume, after optionalpreliminary treatment, generally in the range of between about 0.01 and5 cm³ per gram of carrier, with the diameter of the pores being ingeneral about 2 and 2,000 nm. Preferably, a carrier material is used inwhich at least some of the pores have a diameter of less than 10 nm.

The loading of the porous carrier material with the solution of themetallo-organic comples may generally be in the range of between about0.05 and 0.95 cubic centimeters of solution per cubic centimeter of porevolume. Preferably, the catalyst loading applied is between 0.2 and 0.8cubic centimeters of solution per cubic centimeter of pore volume.

As the central metal atom in the catalytically active metallo-organiccomplex, the transition metals of Groups V, VI, VII, and VIII ofMendeleef's periodic system, such as Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd,and Pt, may be considered. Rhodium, cobalt, ruthenium, and iridium havebeen found to be particularly suitable. These metals may also be appliedas a mixture with one another.

As ligands in the aforementioned metallo-organic complex, organiccompounds may be considered that have in the molecule one atom of theGroup VB or VIB of Mendeleef's periodic system with a free electronpair, such as P, S, B, Te, Sb, and As, as well as ligands such as CO, H,and δ- and π-bonded alkenes. Suitable also are, for example, thehalogenides, such as Cl, Br, and H-, tin-, and germanium II halogenides,and radicals such as acetate, propionate, and readily replaceableligands such as acetylacetonate, hydrogen, carbon monoxide,tetrahydrofuran, and diolefine. Suitable complexes that may beconsidered are rhodiumhydridocarbonyltris(triphenylphosphine),cobalthydridotetracarbonyl,rhodiumbis(triphenylphosphine)carbonylchloride,rhodiumhydridobiscarbonylbis(triphenylphosphine) andrhodiumcarbonylchloride-bis(triphenylarsine).

According to the invention, compounds with a vapor pressure of less than1.3 mbar under reaction conditions that are able to function as ligandsin a transition metal complex, may be used as the solvent for the metalcomplex. These ligand-forming compounds (herein also termed "freeligand") used as the solvent, need not be the same as the ligandspresent in the original transition metal complex. They may optionally besubstituted for one or more ligands of the metal complex. It is in factprobable that the catalytically active metal complex will differ underoperational conditions from the metal compound originally dissolved.Suitable ligand-forming compounds for use as the solvent include organiccompounds of phosphorus, antimony, or arsenic. Particularly suitable arephosphorus compounds possessing a free electron pair, such as compoundswith the formula PR¹ R² R³ or P(OR¹)(OR²)(OR³), where R¹, R², and R³represent aliphatic, aromatic, or alkyl aromatic hydrocarbon groups with1-20 carbon atoms. Examples are triethylphosphine, tributylphosphine,tricyclohexylphosphine, methyldiphenylphosphine, diethylphenylphosphine,triphenylphosphine, tri-p-tolylphosphine, trinaphthylphosphine,ethylene-di(dimethylphosphine), trimethylphosphite,trimethylolpropanephosphite, triphenylphosphite, triphenylarsine,phenyldimethylarsine, and triphenylstibine. The high-boilingtriarylphosphines are preferably used.

The concentration of the metallo-organic complex in the free ligand canvary within wide limits. The upper limit is determined by the solubilityof the metallo-organic complex in the free ligand under reactionconditions, while the lower limit is determined mainly by economic andcommercial considerations. The range within which the concentration canthus vary is, for example, from about 10⁻¹ to 10⁻⁵ mole/liter, morepreferably 10⁻² to 10⁻⁴ mole/liter.

To prepare the catalyst, the carrier may be impregnated with a solutionof the catalytically active metal complex or a precursor thereofdissolved in free ligand without other solvents. Just enoughligand-solvent need be used to achieve the desired loading immediately.It is, however, easier to use an auxiliary solvent in the catalystpreparation. When using an auxiliary solvent, the carrier is impregnatedwith a solution of the catalytically active metal complex or a precursorthereof and a mixture of one or more free ligands with a volatileauxiliary solvent, and subsequently the volatile solvent is removed. Byan inert volatile solvent is meant a composition that does not stronglycoordinate with the metallo-organic complex, that has a vapor pressurethat is at least ten times higher than the vapor pressure of the freeligand, and that forms a homogeneous solution with the free ligand andthe metallo-organic complex. Suitable inert volatile solvents include,for example, methanol, ethanol, benzene, toluene, and xylene.

The proportion of free ligand to inert solvent is governed by thecatalyst loading desired. For instance, to obtain a catalyst loading of0.5, 50 percent of the catalyst solution used should consist of volatilesolvent. Just enough catalyst solution is impregnated to fill thecomplete pore volume of the carrier material in the first instance.

If the ligand is present in solid form at room temperature, the mixtureconsisting of metallo-organic complex, free ligand, and inert volatilesolvent, is heated to the temperature at which a homogeneous solution isobtained. The hot, homogeneous catalyst solution is then slowly added tothe carrier material, which has been preheated to a temperature at leastequal to the temperature of the catalyst solution. Atmospheric oxygen isexcluded throughout this mixing, and the mixture is stirred thoroughly.The impregnation may also be performed in a vacuum.

The free-flowing catalyst thus obtained is thereafter freed of volatilesolvent. This can be done by drying the catalyst in vacuo, by thepassage of inert gas, or in situ in the reactor in which thehydroformylation takes place, at a temperature at which the volatilesolvent evaporates. The drying temperature employed is preferably abovethe melting point of the free ligand so that redistribution of the freeligand and the carrier material is already possible during the drying ofthe catalyst.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be elucidated in detail with reference to thefollowing examples of preferred embodiments, without being restricted tothe embodiments described therein.

EXAMPLE I

A catalyst was prepared by impregnating 9.23 g silica (commercialproduct 000-3E, Akzo Chemie Nederland), having a pore volume of 0.85 cm³/g and a particle size between 0.42 and 0.50 mm, with a solution of0.148 g rhodiumhydridoocarbonyltris (triphenylphosphine) in 4.04 gtriphenylphosphine diluted with an equal quantity of benzene.Subsequently, the benzene was evaporated off. The degree of filling ofthe pores with the solution of the rhodium complex was then 50% of thecatalyst thus obtained.

An amount of 4.68 g of the dried catalyst thus obtained was transferredto a reactor. Allyl alcohol was hydroformylated by passing a mixture ofallyl alcohol, hydrogen, and carbon monoxide through the reactor in avolume ratio of 1:4.76:4.76, at a pressure of 3 bar and a temperature of90° C. The total quantity of gas was 66.3 n.ml/minute. The reaction wascarried out continuously for 80 hours. In total, 19.8% of the allylalcohol applied was converted, 18.7% into 2-hydroxytetrahydrofuran, and1.1% into propionaldehyde. The selectivity of the hydroformylation wastherefore 94.4%. Other products were not found. The activity of thecatalyst is 3.4 n.ml allyl alcohol converted per g rhodium (as metal)per second.

EXAMPLE II

A catalyst was prepared in the manner described in Example I byimpregnating 8.9 g silica S with a solution of 0.133 grhodiumhydridocarbonyltris (triphenylphosphine) in 3.22 gtriphenylphosphine and benzene followed by the evaporation of thebenzene. The degree of filling of the pores was 50%. Silica S is anNa-deficient silica (96 ppm Na) that has been heated for 5 hours at 850°C. The surface area is 100 m² /g, the pore volume 0.99 cm³ /g and themean particle diameter (dV/dR)_(max) is 17 nm. The fraction having aparticle size of 1.2 to 1.7 nm was used.

Of the catalyst thus obtained, 5.86 g was transferred to a reactor. Amixture of allyl alcohol, hydrogen, and carbon monoxide in a volumeratio of 1:7.69:7.69 was passed for 62 hours through the reactor at 90°C. and a pressure of 3 bar. The total quantity of gas was 85.2nml/minute. The conversion of allyl alcohol was 30.6%, with 95%selectivity towards 2-hydroxytetrahydrofuran and 5% towardspropionaldehyde. The activity was 3.72 ml allyl alcohol converted per gRh per second.

Subsequently, a mixture of allyl alcohol, hydrogen, and carbon monoxidein a volume ratio of 1:3.81:3.81 was passed at a quantity of 90.5nml/minute through the reactor for 62 hours at 110° C. and 3 bar. Theconversion was 17.9%, the selectivity towards 2-hydroxytetrahydrofuranwas 97.8%, and the activity was 5.06 nml allyl alcohol converted per gRh per second.

EXAMPLE III

A catalyst was prepared in the manner described in Example I byimpregnating 8.84 g silica S with a solution of 0.986 grhodiumhydridocarbonyltris (triphenylphosphine) in 3.31 gtri-p-tolylphosphine. The degree of catalyst loading was 50%.

A mixture of allyl alcohol, hydrogen, and carbon monoxide in a volumeratio of 1:7.73:7.73 was passed through the reactor, in which 3.1 gcatalyst had been introduced, at 88° C. and 4 bar at a quantity of 90.5nml/minute. The conversion was 6.3%, the selectivity towards2-hydroxytetrahydrofuran was 81%, and the activity was 1.91 ml allylalcohol converted per g Rh per second. The duration of the test was 95hours.

With an increase of the temperature to 108° C., other reactionconditions remaining the same, the conversation became 13.2%, theselectivity toward 2-hydroxytetrahydrofuran became 79.5%, and theactivity became 3.93 nml allyl alcohol converted per g Rh per second.The duration of this higher temperature test was 65 hours.

Subsequently, 172.8 nml/minute of a gaseous mixture of allyl alcohol,hydrogen, and carbon monoxide in a volume ratio of 1:7.50:7.50 waspassed through the reactor at 108° C. and 4 bar. The conversion was26.7%, the selectivity 89.8%, and the activity was 11.03 nml allylalcohol converted per g Rh per second. The duration of this latter testwas 80 hours.

In all cases in the above Examples, propionaldehyde was the onlyby-product that could be found in the reaction product. Formation ofthis by-product is countered by using a sodium-deficient carriermaterial. In these 60 to 95 hour tests, no loss of phosphine ormetallo-organic complex was observed, and the activity and selectivityremained constant.

What is claimed is:
 1. An improved process for the conversion of allylalcohol with hydrogen and carbon monoxide in the presence of acatalytically active metallo-organic complex to form a reaction mixturecontaining hydroformylation product selected from the group consistingof 2-hydroxytetrahydrofuran and 4-hydroxybutyraldehyde, the improvementcomprising bringing said allyl alcohol, hydrogen, and carbon monoxide,in a gaseous phase and at a temperature of between about 90° C. and 150°C., into contact with a catalyst comprised of a solid porous carriermaterial containing within its pores a solution of a catalyticallyactive metallo-organic complex in at least one ligand-forming compound,said solution having a vapor pressure of less than 1.3 mbar under thereaction conditions applied.
 2. The process of claim 1 wherein saidallyl alcohol, hydrogen, and carbon monoxide are continuously introducedinto a reaction zone containing said catalyst, and said hydroformylationproduct containing reaction mixture is continuously withdrawn from saidreaction zone.
 3. The process of claim 1 or 2 wherein the conversion isperformed at a temperature of between 100° C. and 130° C.
 4. The processof claim 1 or 2 wherein said conversion is performed at a pressure ofbetween 2 and 5 bar.
 5. The process of claim 1 or 2 wherein the molarratio between hydrogen, allyl alcohol, and carbon dioxide brought intocontact with said catalyst is about 2 to 10:1:2 to
 10. 6. The process ofclaim 5 wherein the molar ratio between hydrogen and carbon monoxide isbetween about 1:1 to 1:5.
 7. The process of claim 1 or 2 wherein saidcarrier material has an organophilic surface that is at leastsubstantially free of acid groups, basic groups and alkali metal ions.8. The process of claim 1 or 2 wherein said ligand-forming compoundwithin which said catalytically active metallo-organic complex isdissolved is a triarylphosphine.